Information on the allowed functions

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GNU Readline Library

Function	Header File	Signature	Summary	Error Return Value
readline	readline/readline.h	char *readline(const char *prompt);	Reads a line from stdin, with line editing and history support.	NULL (on EOF or error)
rl_clear_history	readline/readline.h	void rl_clear_history(void);	Clears the history list.	N/A
rl_on_new_line	readline/readline.h	void rl_on_new_line(void);	Informs readline that the cursor has moved to a new line.	N/A
rl_replace_line	readline/readline.h	void rl_replace_line(const char *text, int clear_undo);	Replaces the current line with text.	N/A
rl_redisplay	readline/readline.h	void rl_redisplay(void);	Redraws the current input line.	N/A
add_history	readline/history.h	void add_history(const char *string);	Adds a line to the history list.	N/A

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Standard C Library

Function	Header File	Signature	Summary	Error Return Value
printf	stdio.h	int printf(const char *format, ...);	Prints formatted output to stdout.	Negative value (on error)
malloc	stdlib.h	void *malloc(size_t size);	Allocates memory on the heap.	NULL (on error)
free	stdlib.h	void free(void *ptr);	Frees previously allocated memory.	N/A

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POSIX System Calls

Function	Header File	Signature	Summary	Error Return Value
write	unistd.h	ssize_t write(int fd, const void *buf, size_t count);	Writes data to a file descriptor.	-1 (on error, sets errno)
access	unistd.h	int access(const char *pathname, int mode);	Checks file accessibility.	-1 (on error, sets errno)
open	fcntl.h	int open(const char *pathname, int flags, ...);	Opens a file or device.	-1 (on error, sets errno)
read	unistd.h	ssize_t read(int fd, void *buf, size_t count);	Reads data from a file descriptor.	-1 (on error, sets errno)
close	unistd.h	int close(int fd);	Closes a file descriptor.	-1 (on error, sets errno)
fork	unistd.h	pid_t fork(void);	Creates a new process by duplicating the calling process.	-1 (on error, sets errno)
wait	sys/wait.h	pid_t wait(int *wstatus);	Waits for a child process to terminate.	-1 (on error, sets errno)
waitpid	sys/wait.h	pid_t waitpid(pid_t pid, int *wstatus, int options);	Waits for a specific child process.	-1 (on error, sets errno)
wait3	sys/wait.h	pid_t wait3(int *wstatus, int options, struct rusage *rusage);	Waits for a child process and returns resource usage.	-1 (on error, sets errno)
wait4	sys/wait.h	pid_t wait4(pid_t pid, int *wstatus, int options, struct rusage *rusage);	Waits for a specific child process and returns resource usage.	-1 (on error, sets errno)
signal	signal.h	void (*signal(int signum, void (*handler)(int)))(int);	Sets a signal handler.	SIG_ERR (on error)
sigaction	signal.h	int sigaction(int signum, const struct sigaction *act, struct sigaction *oldact);	Examines and changes signal action.	-1 (on error, sets errno)
sigemptyset	signal.h	int sigemptyset(sigset_t *set);	Initializes a signal set to empty.	-1 (on error, sets errno)
sigaddset	signal.h	int sigaddset(sigset_t *set, int signum);	Adds a signal to a signal set.	-1 (on error, sets errno)
kill	signal.h	int kill(pid_t pid, int sig);	Sends a signal to a process or process group.	-1 (on error, sets errno)
exit	stdlib.h	void exit(int status);	Terminates the calling process.	N/A
getcwd	unistd.h	char *getcwd(char *buf, size_t size);	Gets the current working directory.	NULL (on error, sets errno)
chdir	unistd.h	int chdir(const char *path);	Changes the current working directory.	-1 (on error, sets errno)
stat	sys/stat.h	int stat(const char *pathname, struct stat *statbuf);	Gets file status.	-1 (on error, sets errno)
lstat	sys/stat.h	int lstat(const char *pathname, struct stat *statbuf);	Gets file status (does not follow symlinks).	-1 (on error, sets errno)
fstat	sys/stat.h	int fstat(int fd, struct stat *statbuf);	Gets file status for an open file descriptor.	-1 (on error, sets errno)
unlink	unistd.h	int unlink(const char *pathname);	Deletes a file.	-1 (on error, sets errno)
execve	unistd.h	int execve(const char *pathname, char *const argv[], char *const envp[]);	Executes a program.	-1 (on error, sets errno)
dup	unistd.h	int dup(int oldfd);	Duplicates a file descriptor.	-1 (on error, sets errno)
dup2	unistd.h	int dup2(int oldfd, int newfd);	Duplicates a file descriptor to a specified number.	-1 (on error, sets errno)
pipe	unistd.h	int pipe(int pipefd[2]);	Creates a pipe.	-1 (on error, sets errno)
opendir	dirent.h	DIR *opendir(const char *name);	Opens a directory stream.	NULL (on error, sets errno)
readdir	dirent.h	struct dirent *readdir(DIR *dirp);	Reads a directory entry.	NULL (on error or end of directory)
closedir	dirent.h	int closedir(DIR *dirp);	Closes a directory stream.	-1 (on error, sets errno)

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Terminal and Environment

Function	Header File	Signature	Summary	Error Return Value
strerror	string.h	char *strerror(int errnum);	Returns a string describing an error number.	Never fails (may return "Unknown error")
perror	stdio.h	void perror(const char *s);	Prints a descriptive error message to stderr.	N/A
isatty	unistd.h	int isatty(int fd);	Checks if a file descriptor is associated with a terminal.	0 (on error or if not a terminal)
ttyname	unistd.h	char *ttyname(int fd);	Returns the name of a terminal.	NULL (on error, sets errno)
ttyslot	unistd.h	int ttyslot(void);	Returns the slot of the current user's terminal in the utmp file.	0 (on error)
ioctl	sys/ioctl.h	int ioctl(int fd, unsigned long request, ...);	Controls device parameters.	-1 (on error, sets errno)
getenv	stdlib.h	char *getenv(const char *name);	Gets an environment variable.	NULL (if variable not found)

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Terminal Control and Termcap

Function	Header File	Signature	Summary	Error Return Value
tcsetattr	termios.h	int tcsetattr(int fd, int optional_actions, const struct termios *termios_p);	Sets terminal attributes.	-1 (on error, sets errno)
tcgetattr	termios.h	int tcgetattr(int fd, struct termios *termios_p);	Gets terminal attributes.	-1 (on error, sets errno)
tgetent	term.h	int tgetent(char *bp, const char *name);	Reads a termcap entry.	-1 or 0 (on error)
tgetflag	term.h	int tgetflag(char *id);	Gets a boolean termcap capability.	-1 (on error)
tgetnum	term.h	int tgetnum(char *id);	Gets a numeric termcap capability.	-1 (on error)
tgetstr	term.h	char *tgetstr(char *id, char **area);	Gets a string termcap capability.	NULL (on error)
tgoto	term.h	char *tgoto(const char *cap, int col, int row);	Expands a termcap cursor addressing string.	NULL (on error)
tputs	term.h	int tputs(const char *str, int affcnt, int (*putc)(int));	Applies padding information to a termcap string.	-1 (on error)

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